1. Field of the Invention
The present invention related to a three dimensional display control apparatus which controls stereo vision parameters in order to display a subject upon a stereo three dimensional display.
2. Description of Related Art
Conventionally, a stereo three dimensional display apparatus which displays a subject upon a stereo three dimensional display has been known, and generally, in a three dimensional display control apparatus which performs output control for such a display device, software such as VRML (Virtual Reality Modeling Language) is employed for performing three dimensional display of CG data.
In the case of performing stereo display, when the same point of a subject in three dimensional space is being displayed by the three dimensional display control apparatus, its positions upon the image for the right eye and upon the image for the left eye are usually different. The user or observer apprehends the distance to the above-mentioned point by merging in his brain these two images whose positions are different (refer to FIGS. 2A to 2C).
There are various stereo vision parameters such as base line length and angle of convergence. When one or more of these parameters are changed, the positions upon the display screen for the left eye and for the right eye vary, even though the point is the same. When this occurs, as a result, the observer comes to feel that the distance to the above-mentioned point has altered. For example, increase of the base line length corresponds to increase in the stature of the observer such that he/she feels as if he/she were a giant, while decrease of the base line length corresponds to decrease in his stature such that he/she feels as if he/she were a dwarf. In such a case, since of course the subject under observation is a body whose size cannot change, the observer feels that the body has become closer or further away with respect to himself, since his actual size cannot change although his subjective size changes.
Although the most suitable value of a stereo vision parameter varies according to the scene in question, this is because the observer can no longer merge the left and right images when the stereo vision of the left and right images is unduly emphasized. In order for the observer to experience the stereo vision of the left and right images without any feeling of uneasiness, it is necessary for all the bodies in the viewing volume (which is the range which can be seen from his eyes) or a portion to which he is directing most attention, to be at a distance equal or greater from the observer to or than a certain predetermined distance (hereinafter referred to as the limit stereographic viewing distance); the stereo vision impression of the left and right images becomes stronger, the closer to the observer are the bodies, or the portions thereof to which the observer is principally directing his attention. The limit stereographic viewing distance is determined by physical characteristics of the display device and by the personal tastes of the observer.
In other words, in the case of a stationary scene, for the observer to perform stereographic viewing of left and right images most effectively without any feeling of uneasiness, it is desirable for the body closest to the observer in his viewing volume, or the portion thereof to which he is principally directing his attention, to be positioned at a spot which is distant from the observer by just the limit stereographic viewing distance. In this manner, the most suitable value of the stereo vision parameter is determined by taking as a standard that one among the bodies present in the viewing volume which is closest to the observer's eyes, or that one which is considered to be the subject of attention. The most suitable value of the stereo vision parameter will be hereinafter referred to as “the most suitable stereo vision parameter value”.
Among conventional three dimensional display control apparatuss, such devices which perform stereo vision parameter control by automatic control, the most suitable stereo vision parameter value is calculated for each frame, and the body scene is displayed in stereo by successively setting the stereo vision parameter for the current frame to the above-mentioned most suitable suitable stereo vision parameter value.
However, with the above described conventional type three dimensional display control apparatuss, since the stereo vision parameter for the current frame is set instantaneously or immediately to the most suitable stereo vision parameter value, if a body should abruptly intrude into the viewing volume, or should leave the viewing volume, it may happen that the most suitable stereo vision parameter value changes abruptly.
When the stereo vision parameter changes, it is also necessary for the observer to adapt himself/herself for stereo vision. In particular, if large changes occur which are abrupt or discontinuous over time, the observer needs to take very great trouble to perform the instantaneous adaptation which is required. And if this is repeated, he/she can experience considerable pain. Furthermore, depending upon circumstances, it may happen that stereo vision becomes impossible, because it is not possible to keep up with abrupt changes of the stereo vision parameter.